Solid Electrolytic Capacitor for Use in Extreme Conditions

ABSTRACT

A capacitor assembly that is capable of performing under extreme conditions, such as at high temperatures and/or high voltages, is provided. The ability to perform at high temperature is achieved in part by enclosing and hermetically sealing the capacitor element within a housing in the presence of a gaseous atmosphere that contains an inert gas, thereby limiting the amount of oxygen and moisture supplied to the solid electrolyte of the capacitor element. Furthermore, the present inventors have also discovered that the ability to perform at high voltages can be achieved through a unique and controlled combination of features relating to the formation of the anode, dielectric, and solid electrolyte. For example, the solid electrolyte is formed from a combination of a conductive polymer and a hydroxy-functional nonionic polymer.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 61/778,848 (filed on Mar, 13, 2013) and which is incorporatedherein in its entirety by reference thereto.

BACKGROUND OF THE INVENTION

Electrolytic capacitors (e.g., tantalum capacitors) are increasinglybeing used in the design of circuits due to their volumetric efficiency,reliability, and process compatibility. For example, one type ofcapacitor that has been developed is a solid electrolytic capacitor thatincludes an anode (e.g., tantalum), a dielectric oxide film (e.g.,tantalum pentoxide, Ta₂O₅) formed on the anode, a solid electrolytelayer, and a cathode. The solid electrolyte layer may be formed from aconductive polymer, such as described in U.S. Pat. No. 5,457,862 toSakata, et al., U.S. Pat. No. 5,473,503 to Sakata, et al., U.S. Pat. No.5,729,428 to Sakata, et al., and U.S. Pat. No. 5,812,367 to Kudoh, etal. Unfortunately, however, the stability of such solid electrolytes ispoor at high temperatures due to the tendency to transform from a dopedto an un-doped state, or vice versa. In response to these and otherproblems, capacitors have been developed that are hermetically sealed tolimit the contact of oxygen with the conductive polymer during use. U.S.Patent Publication No. 2009/0244812 to Rawal, et al., for instance,describes a capacitor assembly that includes a conductive polymercapacitor that is enclosed and hermetically sealed within a ceramichousing in the presence of an inert gas. According to Rawal, et al., theceramic housing limits the amount of oxygen and moisture supplied to theconductive polymer so that it is less likely to oxidize in hightemperature environments, thus increasing the thermal stability of thecapacitor assembly. Despite the benefits achieved, however, problemsnevertheless remain. For example, the capacitor can sometimes becomeinstable under extreme conditions (e.g., high temperature of above about175° C. and/or high voltage of above about 35 volts), leading to poorelectrical performance.

As such, a need currently exists for a solid electrolytic capacitorassembly having improved performance under extreme conditions.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitorassembly is disclosed that comprises a capacitor element, housing, anodetermination, and cathode termination. The capacitor element comprises asintered porous anode body, a dielectric layer that overlies the anodebody, and a solid electrolyte overlying the dielectric layer. The solidelectrolyte comprises a conductive polymer and a hydroxyl-functionalnonionic polymer. A housing defines an interior cavity within which thecapacitor element is positioned and hermetically sealed, wherein theinterior cavity has a gaseous atmosphere that contains an inert gas.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a capacitorassembly of the assembly of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of a capacitorassembly of the assembly of the present invention;

FIG. 3 is a cross-sectional view of yet another embodiment of acapacitor assembly of the assembly of the present invention; and

FIG. 4 is a top view of still another embodiment of a capacitor assemblyof the assembly of the present invention.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a capacitorassembly that is capable of performing under extreme conditions, such asat high temperatures and/or high voltages. The ability to perform athigh temperature is achieved in part by enclosing and hermeticallysealing the capacitor element within a housing in the presence of agaseous atmosphere that contains an inert gas, thereby limiting theamount of oxygen and moisture supplied to the solid electrolyte of thecapacitor element. Furthermore, the present inventors have alsodiscovered that the ability to perform at high voltages can be achievedthrough a unique and controlled combination of features relating to theformation of the anode, dielectric, and solid electrolyte. For example,the solid electrolyte is formed from a combination of a conductivepolymer and a hydroxy-functional nonionic polymer. Without intending tobe limited by theory, it is believed that hydroxy-functional nonionicpolymers can improve the degree of contact between the polymer particlesand the surface of the internal dielectric, which is typicallyrelatively smooth in nature as a result of higher forming voltages. Thisunexpectedly increases the breakdown voltage and wet-to-dry capacitanceof the resulting capacitor.

As a result of the present invention, the capacitor assembly may exhibitexcellent electrical properties even when exposed to high temperatureand/or high voltage environments. For example, the capacitor assemblymay exhibit a relatively high “breakdown voltage” (voltage at which thecapacitor fails), such as about 35 volts or more, in some embodimentsabout 50 volts or more, in some embodiments about 60 volts or more, andin some embodiments, from about 60 volts to about 100 volts, such asdetermined by increasing the applied voltage in increments of 3 voltsuntil the leakage current reaches 1 mA. Likewise, the capacitor may alsobe able to withstand relatively high surge currents, which is alsocommon in high voltage applications. The peak surge current may, forexample, about 2 times the rated voltage or more, such as range fromabout 40 Amps or more, in some embodiments about 60 Amps or more, and insome embodiments, and in some embodiments, from about 120 Amps to about250 Amps. The capacitor may also exhibit a relatively high capacitance.The dry capacitance may be relatively similar to the wet capacitance,which enables the capacitor to have only a small capacitance loss and/orfluctuation in the presence of atmosphere humidity. This performancecharacteristic is quantified by the “wet-to-dry capacitance percentage”,which is determined by the equation:

Wet-to-Dry Capacitance=(Dry Capacitance/Wet Capacitance)×100

For instance, the capacitor assembly may exhibit a wet-to-drycapacitance percentage of about 50% or more, in some embodiments about60% or more, in some embodiments about 70% or more, and in someembodiments, from about 80% to 100%. The capacitor assembly may alsomaintain a low equivalence series resistance (“ESR”), such as less thanabout 100 mohms, in some embodiments less than about 75 mohms, in someembodiments from about 0.01 to about 60 mohms, and in some embodiments,from about 0.05 to about 50 mohms, measured at an operating frequency of100 kHz. In certain cases, such improved capacitance and ESR performancecan remain stable under a variety of temperature different conditions.For example, the capacitance and/or equivalent series resistance of thecapacitor may even be maintained after aging for a substantial amount oftime at high temperatures. For example, the values may be maintained forabout 100 hours or more, in some embodiments from about 300 hours toabout 3000 hours, and in some embodiments, from about 400 hours to about2500 hours (e.g., 500 hours, 600 hours, 700 hours, 800 hours, 900 hours,1000 hours, 1100 hours, 1200 hours, or 2000 hours) at temperaturesranging from about 100° C. to about 250° C., and, in some embodimentsfrom about 100° C. to about 240° C., in some embodiments, from about100° C. to about 230° C., and in some embodiments, from about 175° C. toabout 225° C. (e.g., 175° C. or 200′C).

Various embodiments of the present invention will now be described inmore detail.

-   I. Capacitor Element

A. Anode

The anode body of the anode is formed from a valve metal composition.The specific charge of the composition may vary, such as from about2,000 μF*V/g to about 150,000 μF*V/g, in some embodiments from about3,000 μF*V/g to about 70,000 μF*V/g or more, and in some embodiments,from about 4,000 to about 50,000 μF*V/g. As is known in the art, thespecific charge may be determined by multiplying capacitance by theanodizing voltage employed, and then dividing this product by the weightof the anodized electrode body.

The valve metal composition generally contains a valve metal (i.e.,metal that is capable of oxidation) or valve metal-based compound, suchas tantalum, niobium, aluminum, hafnium, titanium, alloys thereof,oxides thereof, nitrides thereof, and so forth. For example, the valvemetal composition may contain an electrically conductive oxide ofniobium, such as niobium oxide having an atomic ratio of niobium tooxygen of 1:1.0±1.0, in some embodiments 1:1.0±0.3, in some embodiments1:1.0±0.1, and in some embodiments, 1:1.0±0.05. The niobium oxide may beNbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. Examples of such valve metaloxides are described in U.S. Pat. Nos. 6,322,912 to Fife; U.S. Pat. No.6,391,275 to Fife et al.; U.S. Pat. No. 6,416,730 to Fife et al.; U.S.Pat. No. 6,527,937 to Fife; U.S. Pat. No. 6,576,099 to Kimmel, et al.;U.S. Pat. No. 6,592,740 to Fife, et al.; and U.S. Pat. No. 6,639,787 toKimmel, et al., and U.S. Pat. No. 7,220,397 to Kimmel, et al., as wellas U.S. Patent Application Publication Nos. 2005/0019581 to Schnitter;2005/0103638 to Schnitter, et al.; 2005/0013765 to Thomas, et al.

To form the anode body, a powder of the valve metal composition isgenerally employed. The powder may contain particles any of a variety ofshapes, such as nodular, angular, flake, etc., as well as mixturesthereof. In particular embodiments, the particles can have a flake-likemorphology in that they possess a relatively flat or platelet shape.Such particles can provide a short transmission line between the outersurface and interior of the anode and also provide a highly continuousand dense wire-to-anode connection with high conductivity. Among otherthings, this may help increase the breakdown voltage (voltage at whichthe capacitor fails) and help lower equivalent series resistance(“ESR”). The particles may also increase the specific charge of theanode when anodized at higher voltages, thereby increasing energydensity.

When employed, the flake particles are generally flat. The degree offlatness is generally defined by the “aspect ratio”, i.e., the averagediameter or width of the particles divided by the average thickness(“D/T”). For example, the aspect ratio of the particles may be fromabout 2 to about 100, in some embodiments from about 3 to about 50, insome embodiments, from about 4 to about 30. The particles may also havea specific surface area of from about 0.5 to about 10.0 m²/g, in someembodiments from about 0.7 to about 5.0 m²/g, and in some embodiments,from about 1.0 to about 4.0 m²/g. The term “specific surface area”generally refers to surface area as determined by the physical gasadsorption (B.E.T.) method of Bruanauer, Emmet, and Teller, Journal ofAmerican Chemical Society, Vol. 60, 1938, p. 309, with nitrogen as theadsorption gas. The test may be conducted with a MONOSORB® SpecificSurface Area Analyzer available from QUANTACHROME Corporation, Syosset,N.Y., which measures the quantity of adsorbate nitrogen gas adsorbed ona solid surface by sensing the change in thermal conductivity of aflowing mixture of adsorbate and inert carrier gas (e.g., helium).

The bulk density (also known as Scott density) is also typically fromabout 0.1 to about 2 grams per cubic centimeter (g/cm³), in someembodiments from about 0.2 g/cm³ to about 1.5 g/cm³, and in someembodiments, from about 0.4 g/cm³ to about 1 g/cm³. “Bulk density” maybe determined using a flow meter funnel and density cup. Morespecifically, the powder sample may be poured through the funnel intothe cup until the sample completely fills and overflows the periphery ofthe cup, and thereafter sample may be leveled-off by a spatula, withoutjarring, so that it is flush with the top of the cup. The leveled sampleis transferred to a balance and weighed to the nearest 0.1 gram todetermine the density value. Such an apparatus is commercially availablefrom Alcan Aluminum Corp. of Elizabeth, N.J. The particles may also havean average size (e.g., width) of from about 0.1 to about 100micrometers, in some embodiments from about 0.5 to about 70 micrometers,and in some embodiments, from about 1 to about 50 micrometers.

Certain additional components may also be included in the powder. Forexample, the powder may be optionally mixed with a binder and/orlubricant to ensure that the particles adequately adhere to each otherwhen pressed to form the anode body. Suitable binders may include, forinstance, poly(vinyl butyral);

poly(vinyl acetate); poly(vinyl alcohol); poly(vinyl pyrrolidone);cellulosic polymers, such as carboxymethylcellulose, methyl cellulose,ethyl cellulose, hydroxyethyl cellulose, and methylhydroxyethylcellulose; atactic polypropylene, polyethylene; polyethylene glycol(e.g., Carbowax from Dow Chemical Co.); polystyrene,poly(butadiene/styrene); polyamides, polyimides, and polyacrylamides,high molecular weight polyethers; copolymers of ethylene oxide andpropylene oxide; fluoropolymers, such as polytetrafluoroethylene,polyvinylidene fluoride, and fluoro-olefin copolymers; acrylic polymers,such as sodium polyacrylate, poly(lower alkyl acrylates), poly(loweralkyl methacrylates) and copolymers of lower alkyl acrylates andmethacrylates; and fatty acids and waxes, such as stearic and othersoapy fatty acids, vegetable wax, microwaxes (purified paraffins), etc.The binder may be dissolved and dispersed in a solvent. Exemplarysolvents may include water, alcohols, and so forth. When utilized, thepercentage of binders and/or lubricants may vary from about 0.1% toabout 8% by weight of the total mass. It should be understood, however,that binders and/or lubricants are not necessarily required in thepresent invention.

The resulting powder may then be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead (e.g., tantalumwire). It should be further appreciated that the anode lead mayalternatively be attached (e.g., welded) to the anode body subsequent topressing and/or sintering of the anode body.

After compaction, the resulting anode body may then be diced into anydesired shape, such as square, rectangle, circle, oval, triangle,hexagon, octagon, heptagon, pentagon, etc. The anode body may also havea “fluted” shape in that it contains one or more furrows, grooves,depressions, or indentations to increase the surface to volume ratio tominimize ESR and extend the frequency response of the capacitance. Theanode body may then be subjected to a heating step in which most, if notall, of any binder/lubricant are removed. For example, the anode body istypically heated by an oven that operates at a temperature of from about150° C. to about 500° C. Alternatively, the binder/lubricant may also beremoved by contacting the pellet with an aqueous solution, such asdescribed in U.S. Pat. No. 6,197,252 to Bishop et. al. Thereafter, theporous body is sintered to form an integral mass. The temperature,atmosphere, and time of the sintering may depend on a variety offactors, such as the type of anode, the size of the anode, etc.Typically, sintering occurs at a temperature of from about from about800° C. to about 1900° C., in some embodiments from about 1000° C. toabout 1500° C., and in some embodiments, from about 1100° C. to about1400° C., for a time of from about 5 minutes to about 100 minutes, andin some embodiments, from about 30 minutes to about 60 minutes. Ifdesired, sintering may occur in an atmosphere that limits the transferof oxygen atoms to the anode. For example, sintering may occur in areducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc. Thereducing atmosphere may be at a pressure of from about 10 Torr to about2000 Torr, in some embodiments from about 100 Torr to about 1000 Torr,and in some embodiments, from about 100 Torr to about 930 Torr. Mixturesof hydrogen and other gases (e.g., argon or nitrogen) may also beemployed.

The resulting anode may have a relatively low carbon and oxygen content.For example, the anode may have no more than about 50 ppm carbon, and insome embodiments, no more than about 10 ppm carbon. Likewise, the anodemay have no more than about 3500 ppm oxygen, in some embodiments no morethan about 3000 ppm oxygen, and in some embodiments, from about 500 toabout 2500 ppm oxygen. Oxygen content may be measured by LECO OxygenAnalyzer and includes oxygen in natural oxide on the tantalum surfaceand bulk oxygen in the tantalum particles. Bulk oxygen content iscontrolled by period of crystalline lattice of tantalum, which isincreasing linearly with increasing oxygen content in tantalum until thesolubility limit is achieved. This method was described in “CriticalOxygen Content In Porous Anodes Of Solid Tantalum Capacitors”,Pozdeev-Freeman et al., Journal of Materials Science: Materials InElectronics 9, (1998) 309-311 wherein X-ray diffraction analysis (XRDA)was employed to measure period of crystalline lattice of tantalum.Oxygen in sintered tantalum anodes may be limited to thin naturalsurface oxide, while the bulk of tantalum is practically free of oxygen.

As noted above, an anode lead may also be connected to the anode bodythat extends in a longitudinal direction therefrom. The anode lead maybe in the form of a wire, sheet, etc., and may be formed from a valvemetal compound, such as tantalum, niobium, niobium oxide, etc.Connection of the lead may be accomplished using known techniques, suchas by welding the lead to the body or embedding it within the anode bodyduring formation (e.g., prior to compaction and/or sintering).

B. Dielectric.

A dielectric also overlies or coats the anode body. The dielectric maybe formed by anodically oxidizing (“anodizing”) the sintered anode sothat a dielectric layer is formed over and/or within the anode body. Forexample, a tantalum (Ta) anode body may be anodized to tantalumpentoxide (Ta₂O₅). Typically, anodization is performed by initiallyapplying a solution to the anode body, such as by dipping the anode bodyinto the electrolyte. A solvent is generally employed, such as water(e.g., deionized water). To enhance ionic conductivity, a compound maybe employed that is capable of dissociating in the solvent to form ions.Examples of such compounds include, for instance, acids, such asdescribed below with respect to the electrolyte. For example, an acid(e.g., phosphoric acid) may constitute from about 0.01 wt. % to about 5wt. %, in some embodiments from about 0.05 wt. % to about 0.8 wt. %, andin some embodiments, from about 0.1 wt. % to about 0.5 wt. % of theanodizing solution. If desired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode body. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 9 toabout 200 V, and in some embodiments, from about 20 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode body and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode body in that itpossesses a first portion that overlies an external surface of the anodebody and a second portion that overlies an interior surface of the anodebody. In such embodiments, the first portion is selectively formed sothat its thickness is greater than that of the second portion. It shouldbe understood, however, that the thickness of the dielectric layer neednot be uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process is generally employed. In each stage of the process,the sintered anode body is anodically oxidized (“anodized”) to form adielectric layer (e.g., tantalum pentoxide). During the first stage ofanodization, a relatively small forming voltage is typically employed toensure that the desired dielectric thickness is achieved for the innerregion, such as forming voltages ranging from about 1 to about 90 volts,in some embodiments from about 2 to about 50 volts, and in someembodiments, from about 5 to about 20 volts. Thereafter, the sinteredbody may then be anodically oxidized in a second stage of the process toincrease the thickness of the dielectric to the desired level. This isgenerally accomplished by anodizing in an electrolyte at a highervoltage than employed during the first stage, such as at formingvoltages ranging from about 50 to about 350 volts, in some embodimentsfrom about 60 to about 300 volts, and in some embodiments, from about 70to about 200 volts. During the first and/or second stages, theelectrolyte may be kept at a temperature within the range of from about15° C. to about 95° C., in some embodiments from about 20° C. to about90° C., and in some embodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however, itis desired to employ different solutions to help better facilitate theattainment of a higher thickness at the outer portions of the dielectriclayer. For example, it may be desired that the electrolyte employed inthe second stage has a lower ionic conductivity than the electrolyteemployed in the first stage to prevent a significant amount of oxidefilm from forming on the internal surface of anode body. In this regard,the electrolyte employed during the first stage may contain an acidiccompound, such as hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage typically contains a salt of a weak acid so that thehydronium ion concentration increases in the pores as a result of chargepassage therein. Ion transport or diffusion is such that the weak acidanion moves into the pores as necessary to balance the electricalcharges. As a result, the concentration of the principal conductingspecies (hydronium ion) is reduced in the establishment of equilibriumbetween the hydronium ion, acid anion, and undissociated acid, thusforms a poorer-conducting species. The reduction in the concentration ofthe conducting species results in a relatively high voltage drop in theelectrolyte, which hinders further anodization in the interior while athicker oxide layer is being built up on the outside to a higherformation voltage in the region of continued high conductivity. Suitableweak acid salts may include, for instance, ammonium or alkali metalsalts (e.g., sodium, potassium, etc.) of boric acid, boronic acid,acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularlysuitable salts include sodium tetraborate and ammonium pentaborate. Suchelectrolytes typically have an electrical conductivity of from about 0.1to about 20 mS/cm, in some embodiments from about 0.5 to about 10 mS/cm,and in some embodiments, from about 1 to about 5 mS/cm, determined at atemperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode body may also be rinsed or washed with another solvent (e.g.,water) after the first and/or second stages to remove the electrolyte.

C. Solid Electrolyte

i. Conductive Polymer

As indicated above, a solid electrolyte overlies the dielectric thatgenerally functions as the cathode for the capacitor. The solidelectrolyte contains a conductive polymer, which is typicallyπ-conjugated and has electrical conductivity after oxidation orreduction, such as an electrical conductivity of at least about 1 μS/cm.Examples of such π-conjugated conductive polymers include, for instance,polyheterocycles (e.g., polypyrroles, polythiophenes, polyanilines,etc.), polyacetylenes, poly-p-phenylenes, polyphenolates, and so forth.In one embodiment, for example, the polymer is a substitutedpolythiophene, such as those having the following general structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₈ aralkylradical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al., which is incorporated herein in its entirety by referencethereto for all purposes, describes various techniques for formingsubstituted polythiophenes from a monomeric precursor. The monomericprecursor may, for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above. In one particular embodiment,“q” is 0. One commercially suitable example of 3,4-ethylenedioxthiopheneis available from H. C. Starck GmbH under the designation Clevios™ M.Other suitable monomers are also described in U.S. Pat. No. 5,111,327 toBlohm, et al. and U.S. Pat. No. 6,635,729 to Groenendaal, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above monomers. Higher molecularderivatives, i.e., tetramers, pentamers, etc. of the monomers aresuitable for use in the present invention. The derivatives may be madeup of identical or different monomer units and used in pure form and ina mixture with one another and/or with the monomers. Oxidized or reducedforms of these precursors may also be employed.

Various methods may be utilized to form the conductive polymer layer.For example, an in situ polymerized layer may be formed by chemicallypolymerizing monomers in the presence of an oxidative catalyst. Theoxidative catalyst typically includes a transition metal cation, such asiron(III), copper(II), chromium(VI), cerium(IV), manganese(IV),manganese(VII), or ruthenium(III) cations, and etc. A dopant may also beemployed to provide excess charge to the conductive polymer andstabilize the conductivity of the polymer. The dopant typically includesan inorganic or organic anion, such as an ion of a sulfonic acid. Incertain embodiments, the oxidative catalyst has both a catalytic anddoping functionality in that it includes a cation (e.g., transitionmetal) and an anion (e.g., sulfonic acid). For example, the oxidativecatalyst may be a transition metal salt that includes iron(III) cations,such as iron(III) halides (e.g., FeCl₃) or iron(III) salts of otherinorganic acids, such as Fe(ClO₄)₃ or Fe₂(SO₄)₃ and the iron(III) saltsof organic acids and inorganic acids comprising organic radicals.Examples of iron(III) salts of inorganic acids with organic radicalsinclude, for instance, iron(III) salts of sulfuric acid monoesters of C₁to C₂₀ alkanols (e.g., iron(III) salt of lauryl sulfate). Likewise,examples of iron(III) salts of organic acids include, for instance,iron(III) salts of C₁ to C₂₀ alkane sulfonic acids (e.g., methane,ethane, propane, butane, or dodecane sulfonic acid); iron(III) salts ofaliphatic perfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid, or perfluorooctane sulfonic acid);iron(III) salts of aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethylhexylcarboxylic acid); iron(III) salts of aliphaticperfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctaneacid); iron(III) salts of aromatic sulfonic acids optionally substitutedby C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid, o-toluenesulfonic acid, p-toluene sulfonic acid, or dodecylbenzene sulfonicacid); iron(III) salts of cycloalkane sulfonic acids (e.g., camphorsulfonic acid); and so forth. Mixtures of these above-mentionediron(III) salts may also be used. Iron(III)-p-toluene sulfonate,iron(III)-o-toluene sulfonate, and mixtures thereof, are particularlysuitable. One commercially suitable example of iron(III)-p-toluenesulfonate is available from Heraeus Clevios under the designationClevios™ C.

The oxidative catalyst and monomer may be applied either sequentially ortogether to initiate the polymerization reaction. Suitable applicationtechniques for applying these components include screen-printing,dipping, electrophoretic coating, and spraying. As an example, themonomer may initially be mixed with the oxidative catalyst to form aprecursor solution. Once the mixture is formed, it may be applied to theanode part and then allowed to polymerize so that a conductive coatingis formed on the surface. Alternatively, the oxidative catalyst andmonomer may be applied sequentially. In one embodiment, for example, theoxidative catalyst is dissolved in an organic solvent (e.g., butanol)and then applied as a dipping solution. The anode part may then be driedto remove the solvent therefrom. Thereafter, the part may be dipped intoa solution containing the monomer. Regardless, polymerization istypically performed at temperatures of from about −10° C. to about 250°C., and in some embodiments, from about 0° C. to about 200° C.,depending on the oxidizing agent used and desired reaction time.Suitable polymerization techniques, such as described above, may bedescribed in more detail in U.S. Pat. No. 7,515,396 to Biler. Stillother methods for applying such conductive coating(s) may be describedin U.S. Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 toSakata, et al., U.S. Pat. No. 5,729,428 to Sakata, et al., and U.S. Pat.No. 5,812,367 to Kudoh, et al., which are incorporated herein in theirentirety by reference thereto for all purposes.

In addition to in situ application, the conductive polymer solidelectrolyte may also be applied in the form of a dispersion ofconductive polymer particles. One benefit of employing a dispersion isthat it may minimize the presence of ionic species (e.g., Fe²⁺ or Fe³⁺)produced during in situ polymerization, which can cause dielectricbreakdown under high electric field due to ionic migration. Thus, byapplying the conductive polymer as a dispersion rather through in situpolymerization, the resulting capacitor may exhibit a relatively high“breakdown voltage.” To enable good impregnation of the anode, theparticles employed in the dispersion typically have a small size, suchas an average size (e.g., diameter) of from about 1 to about 150nanometers, in some embodiments from about 2 to about 50 nanometers, andin some embodiments, from about 5 to about 40 nanometers. The diameterof the particles may be determined using known techniques, such as byultracentrifuge, laser diffraction, etc. The shape of the particles maylikewise vary. In one particular embodiment, for instance, the particlesare spherical in shape. However, it should be understood that othershapes are also contemplated by the present invention, such as plates,rods, discs, bars, tubes, irregular shapes, etc. The concentration ofthe particles in the dispersion may vary depending on the desiredviscosity of the dispersion and the particular manner in which thedispersion is to be applied to the capacitor. Typically, however, theparticles constitute from about 0.1 to about 10 wt. %, in someembodiments from about 0.4 to about 5 wt. %, and in some embodiments,from about 0.5 to about 4 wt. % of the dispersion.

The dispersion also generally contains a counterion that enhances thestability of the particles. That is, the conductive polymer (e.g.,polythiophene or derivative thereof) typically has a charge on the mainpolymer chain that is neutral or positive (cationic). Polythiophenederivatives, for instance, typically carry a positive charge in the mainpolymer chain. In some cases, the polymer may possess positive andnegative charges in the structural unit, with the positive charge beinglocated on the main chain and the negative charge optionally on thesubstituents of the radical “R”, such as sulfonate or carboxylategroups. The positive charges of the main chain may be partially orwholly saturated with the optionally present anionic groups on theradicals “R.” Viewed overall, the polythiophenes may, in these cases, becationic, neutral or even anionic. Nevertheless, they are all regardedas cationic polythiophenes as the polythiophene main chain has apositive charge.

The counterion may be a monomeric or polymeric anion that counteractsthe charge of the conductive polymer. Polymeric anions can, for example,be anions of polymeric carboxylic acids (e.g., polyacrylic acids,polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonic acids(e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids,etc.); and so forth. The acids may also be copolymers, such ascopolymers of vinyl carboxylic and vinyl sulfonic acids with otherpolymerizable monomers, such as acrylic acid esters and styrene.Likewise, suitable monomeric anions include, for example, anions of C₁to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);aliphatic C₁ to C₂₀ carboxylic acids (e.g., 2-ethyl-hexylcarboxylicacid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acidor perfluorooctanoic acid); aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzenesulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acidor tetrafluoroborates, hexafluorophosphates, perchlorates,hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates);and so forth. Particularly suitable counteranions are polymeric anions,such as a polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid (“PSS”)). The molecular weight of such polymeric anionstypically ranges from about 1,000 to about 2,000,000, and in someembodiments, from about 2,000 to about 500,000.

When employed, the weight ratio of such counterions to conductivepolymers in the dispersion and in the resulting layer is typically fromabout 0.5:1 to about 50:1, in some embodiments from about 1:1 to about30:1, and in some embodiments, from about 2:1 to about 20:1. The weightof the electrically conductive polymers corresponds referred to theabove-referenced weight ratios refers to the weighed-in portion of themonomers used, assuming that a complete conversion occurs duringpolymerization.

In addition to conductive polymer(s) and counterion(s), the dispersionmay also contain one or more binders to further enhance the adhesivenature of the polymeric layer and also increase the stability of theparticles within the dispersion. The binders may be organic in nature,such as polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides,polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters,polyacrylic acid amides, polymethacrylic acid esters, polymethacrylicacid amides, polyacrylonitriles, styrene/acrylic acid ester, vinylacetate/acrylic acid ester and ethylene/vinyl acetate copolymers,polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters,polycarbonates, polyurethanes, polyamides, polyimides, polysulfones,melamine formaldehyde resins, epoxide resins, silicone resins orcelluloses. Crosslinking agents may also be employed to enhance theadhesion capacity of the binders. Such crosslinking agents may include,for instance, melamine compounds, masked isocyanates or functionalsilanes, such as 3-glycidoxypropyltrialkoxysilane, tetraethoxysilane andtetraethoxysilane hydrolysate or crosslinkable polymers, such aspolyurethanes, polyacrylates or polyolefins, and subsequentcrosslinking.

Dispersion agents may also be employed to facilitate the formation ofthe solid electrolyte and the ability to apply it to the anode part.Suitable dispersion agents include solvents, such as aliphatic alcohols(e.g., methanol, ethanol, i-propanol and butanol), aliphatic ketones(e.g., acetone and methyl ethyl ketones), aliphatic carboxylic acidesters (e.g., ethyl acetate and butyl acetate), aromatic hydrocarbons(e.g., toluene and xylene), aliphatic hydrocarbons (e.g., hexane,heptane and cyclohexane), chlorinated hydrocarbons (e.g.,dichloromethane and dichloroethane), aliphatic nitriles (e.g.,acetonitrile), aliphatic sulfoxides and sulfones (e.g., dimethylsulfoxide and sulfolane), aliphatic carboxylic acid amides (e.g.,methylacetamide, dimethylacetamide and dimethylformamide), aliphatic andaraliphatic ethers (e.g., diethylether and anisole), water, and mixturesof any of the foregoing solvents. A particularly suitable dispersionagent is water.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Adhesives may also be employed, such as organofunctional silanes ortheir hydrolysates, for example 3-glycidoxypropyltrialkoxysilane,3-aminopropyl-triethoxysilane, 3-mercaptopropyl-trimethoxysilane,3-metacryloxypropyltrimethoxysilane, vinyltrimethoxysilane oroctyltriethoxysilane, The dispersion may also contain additives thatincrease conductivity, such as ether group-containing compounds (e.g.,tetrahydrofuran), lactone group-containing compounds (e.g.,γ-butyrolactone or γ-valerolactone), amide or lactam group-containingcompounds (e.g., caprolactam, N-methylcaprolactam,N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide (DMF),N-methylformamide, N-methylformanilide, N-methylpyrrolidone (NMP),N-octylpyrrolidone, or pyrrolidone), sulfones and sulfoxides (e.g.,sulfolane (tetramethylenesulfone) or dimethylsulfoxide (DMSO)), sugar orsugar derivatives (e.g., saccharose, glucose, fructose, or lactose),sugar alcohols (e.g., sorbitol or mannitol), furan derivatives (e.g.,2-furancarboxylic acid or 3-furancarboxylic acid), an alcohols (e.g.,ethylene glycol, glycerol, di- or triethylene glycol).

The polymeric dispersion may be applied using a variety of knowntechniques, such as by spin coating, impregnation, pouring, dropwiseapplication, injection, spraying, doctor blading, brushing, printing(e.g., ink-jet, screen, or pad printing), or dipping. Although it mayvary depending on the application technique employed, the viscosity ofthe dispersion is typically from about 0.1 to about 100,000 mPas(measured at a shear rate of 100 s⁻¹), in some embodiments from about 1to about 10,000 mPas, in some embodiments from about 10 to about 1,500mPas, and in some embodiments, from about 100 to about 1000 mPas. Onceapplied, the layer may be dried and/or washed. One or more additionallayers may also be formed in this manner to achieve the desiredthickness. Typically, the total thickness of the layer(s) formed by thisparticle dispersion is from about 1 to about 50 μm, and in someembodiments, from about 5 to about 20 μm. The weight ratio ofcounterions to conductive polymers is likewise from about 0.5:1 to about50:1, in some embodiments from about 1:1 to about 30:1, and in someembodiments, from about 2:1 to about 20:1.

ii. Hydroxy-Functional Nonionic Polymer

A hydroxyl-functional nonionic polymer, as described in detail above, isalso included in the solid electrolyte. The term “hydroxy-functional”generally means that the compound contains at least one hydroxylfunctional group or is capable of possessing such a functional group inthe presence of a solvent. Without intending to be limited by theory, itis believed that hydroxy-functional nonionic polymers can improve thedegree of contact between the conductive polymer and the surface of theinternal dielectric, which is typically relatively smooth in nature as aresult of higher forming voltages. This unexpectedly increases thebreakdown voltage and wet-to-dry capacitance of the resulting capacitor.Furthermore, it is believed that the use of a hydroxy-functional polymerwith a certain molecular weight can also minimize the likelihood ofchemical decomposition at high voltages. For instance, the molecularweight of the hydroxy-functional polymer may be from about 100 to 10,000grams per mole, in some embodiments from about 200 to 2,000, in someembodiments from about 300 to about 1,200, and in some embodiments, fromabout 400 to about 800.

Any of a variety of hydroxy-functional nonionic polymers may generallybe employed for this purpose. In one embodiment, for example, thehydroxy-functional polymer is a polyalkylene ether. Polyalkylene ethersmay include polyalkylene glycols (e.g., polyethylene glycols,polypropylene glycols polytetramethylene glycols, polyepichlorohydrins,etc.), polyoxetanes, polyphenylene ethers, polyether ketones, and soforth. Polyalkylene ethers are typically predominantly linear, nonionicpolymers with terminal hydroxy groups. Particularly suitable arepolyethylene glycols, polypropylene glycols and polytetramethyleneglycols (polytetrahydrofurans), which are produced by polyaddition ofethylene oxide, propylene oxide or tetrahydrofuran onto water. Thepolyalkylene ethers may be prepared by polycondensation reactions fromdials or polyols. The diol component may be selected, in particular,from saturated or unsaturated, branched or unbranched, aliphaticdihydroxy compounds containing 5 to 36 carbon atoms or aromaticdihydroxy compounds, such as, for example, pentane-1,5-diol,hexane-1,6-diol, neopentyl glycol, bis-(hydroxymethyl)-cyclohexanes,bisphenol A, dimer diols, hydrogenated dimer diaos or even mixtures ofthe diols mentioned. In addition, polyhydric alcohols may also be usedin the polymerization reaction, including for example glycerol, di- andpolyglycerol, trimethylolpropane, pentaerythritol or sorbitol.

In addition to those noted above, other hydroxy-functional nonionicpolymers may also be employed in the present invention. Some examples ofsuch polymers include, for instance, ethoxylated alkylphenols;ethoxylated or propoxylated C₆-C₂₄ fatty alcohols; polyoxyethyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₂H₄)₁₋₂₅—OH (e.g., octaethylene glycol monododecylether and pentaethylene glycol monododecyl ether); polyoxypropyleneglycol alkyl ethers having the general formula;CH₃—(CH₂)₁₀₋₁₆—(O—C₃H₆)₁₋₂₅—OH; polyoxyethylene glycol octylphenolethers having the following general formula:C₈H₁₇—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., Triton™ X-100); polyoxyethyleneglycol alkylphenol ethers having the following general formula:C₉H₁₉—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., nonoxynol-9); polyoxyethylene glycolesters of C₈-C₂₄ fatty acids, such as polyoxyethylene glycol sorbitanalkyl esters (e.g., polyoxyethylene (20) sorbitan monolaurate,polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20)sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, PEG-20methyl glucose distearate, PEG-20 methyl glucose sesquistearate, PEG-80castor oil, and PEG-20 castor oil, PEG-3 castor oil, PEG 600 dioleate,and PEG 400 dioleate) and polyoxyethylene glycerol alkyl esters (e.g.,polyoxyethylene-23 glycerol laurate and polyoxyethylene-20 glycerolstearate); polyoxyethylene glycol ethers of C₈-C₂₄ fatty acids (e.g.,polyoxyethylene-10 cetyl ether, polyoxyethylene-10 stearyl ether,polyoxyethylene-20 cetyl ether, polyoxyethylene-10 oleyl ether,polyoxyethylene-20 oleyl ether, polyoxyethylene-20 isohexadecyl ether,polyoxyethylene-15 tridecyl ether, and polyoxyethylene-6 tridecylether); block copolymers of polyethylene glycol and polypropylene glycol(e.g., Poloxamers); and so forth, as well as mixtures thereof.

The hydroxy-functional nonionic polymer may be incorporated into thesolid electrolyte in a variety of different ways. In certainembodiments, for instance, the nonionic polymer may simply beincorporated into any conductive polymer layer(s) formed by a method asdescribed above (e.g., in situ polymerization or pre-polymerizedparticle dispersion). In such embodiments, the concentration of thenonionic polymer in the layer may be from about 1 wt. % to about 50 wt.%, in some embodiments from about 5 wt. % to about 40 wt. %, and in someembodiments, from about 10 wt. % to about 30 wt. %.

In other embodiments, however, the nonionic polymer may be applied afterthe initial polymer layer(s) are formed. In such embodiments, thetechnique used to apply the nonionic polymer may vary. For example, thenonionic polymer may be applied in the form of a liquid solution usingvarious methods, such as immersion, dipping, pouring, dripping,injection, spraying, spreading, painting or printing, for example,inkjet, screen printing or tampon printing. Solvents known to the personskilled in the art can be employed in the solution, such as water,alcohols, or a mixture thereof. The concentration of the nonionicpolymer in such a solution typically ranges from about 5 wt. % to about95 wt. %, in some embodiments from about 10 wt. % to about 70 wt. %, andin some embodiments, from about 15 wt. % to about 50 wt. % of thesolution. If desired, such solutions may be generally free of conductivepolymers. For example, conductive polymers may constitute about 2 wt. %or less, in some embodiments about 1 wt. % or less, and in someembodiments, about 0.5 wt. % or less of the solution.

Alternatively, however, it may also be desired to employ a conductivepolymer in combination with the nonionic polymer. For example, incertain embodiments, a “second” layer that contains a conductive (e.g.,in situ polymerized or pre-polymerized particles) and a nonionic polymeris applied to the anode after the “first” layer is applied to the anodebody. When employed, the conductive particles of the second polymerlayer are as described above, although they need not be identical tothose optionally employed in the first layer. Regardless, theconcentration of the nonionic polymer in the second layer is typicallyfrom about 1 wt. % to about 50 wt. %, in some embodiments from about 5wt. % to about 40 wt. %, and in some embodiments, from about 10 wt. % toabout 30 wt. %. Likewise, in those embodiments in which the nonionicpolymer is employed in a second layer, it may also be desirable that thefirst layer is generally free of such nonionic polymers. For example,nonionic polymers may constitute about 2 wt. % or less, in someembodiments about 1 wt. % or less, and in some embodiments, about 0.5wt. % or less of the first layer. Once applied, the second layer may bedried and/or washed. One or more additional layers may also be formed inthis manner to achieve the desired thickness. Typically, the totalthickness of the layers formed by the second polymer dispersion is fromabout 0.1 to about 5 μm, in some embodiments from about 0.1 to about 3μm, and in some embodiments, from about 0.2 to about 1 μm.

D. External Polymer Coating

Although not required, an external polymer coating may also be appliedto the anode body and overlie the solid electrolyte. The externalpolymer coating generally contains one or more layers formed from adispersion of pre-polymerized conductive particles, such as described inmore detail above. The external coating may be able to further penetrateinto the edge region of the capacitor body to increase the adhesion tothe dielectric and result in a more mechanically robust part, which mayreduce equivalent series resistance and leakage current. Because it isgenerally intended to improve the degree of edge coverage rather toimpregnate the interior of the anode body, the particles used in theexternal coating typically have a larger size than those employed in anyoptional dispersions of the solid electrolyte. For example, the ratio ofthe average size of the particles employed in the external polymercoating to the average size of the particles employed in any dispersionof the solid electrolyte is typically from about 1.5 to about 30, insome embodiments from about 2 to about 20, and in some embodiments, fromabout 5 to about 15. For example, the particles employed in thedispersion of the external coating may have an average size of fromabout 50 to about 500 nanometers, in some embodiments from about 80 toabout 250 nanometers, and in some embodiments, from about 100 to about200 nanometers.

If desired, a crosslinking agent may also be employed in the externalpolymer coating to enhance the degree of adhesion to the solidelectrolyte. Typically, the crosslinking agent is applied prior toapplication of the dispersion used in the external coating. Suitablecrosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,4-butanediamine, etc., as well as mixturesthereof.

The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1 toabout 50 μm, in some embodiments from about 2 to about 40 μm, and insome embodiments, from about 5 to about 20 μm.

E. Other Components of the Capacitor

If desired, the capacitor may also contain other layers as is known inthe art. For example, a protective coating may optionally be formedbetween the dielectric and solid electrolyte, such as one made of arelatively insulative resinous material (natural or synthetic). Suchmaterials may have a specific resistivity of greater than about 10 Ω⋅cm,in some embodiments greater than about 100, in some embodiments greaterthan about 1,000 Ω⋅cm, in some embodiments greater than about 1×10⁵Ω⋅cm, and in some embodiments, greater than about 1×10¹⁰ Ω⋅cm. Someresinous materials that may be utilized in the present inventioninclude, but are not limited to, polyurethane, polystyrene, esters ofunsaturated or saturated fatty acids (e.g., glycerides), and so forth.For instance, suitable esters of fatty acids include, but are notlimited to, esters of lauric acid, myristic acid, palmitic acid, stearicacid, eleostearic acid, oleic acid, linoleic acid, linolenic acid,aleuritic acid, shellolic acid, and so forth. These esters of fattyacids have been found particularly useful when used in relativelycomplex combinations to form a “drying oil”, which allows the resultingfilm to rapidly polymerize into a stable layer. Such drying oils mayinclude mono-, di-, and/or tri-glycerides, which have a glycerolbackbone with one, two, and three, respectively, fatty acyl residuesthat are esterified. For instance, some suitable drying oils that may beused include, but are not limited to, olive oil, linseed oil, castoroil, tung oil, soybean oil, and shellac. These and other protectivecoating materials are described in more detail U.S. Pat. No. 6,674,635to Fife, et al., which is incorporated herein in its entirety byreference thereto for all purposes.

If desired, the part may also be applied with a carbon layer (e.g.,graphite) and silver layer, respectively. The silver coating may, forinstance, act as a solderable conductor, contact layer, and/or chargecollector for the capacitor and the carbon coating may limit contact ofthe silver coating with the solid electrolyte. Such coatings may coversome or all of the solid electrolyte.

Generally speaking, the capacitor element is substantially free ofresins (e.g., epoxy resins) that encapsulate the capacitor element asare often employed in conventional solid electrolytic capacitors. Amongother things, the encapsulation of the capacitor element can lead toinstability in extreme environments, i.e., high temperature (e.g., aboveabout 175° C.) and/or high voltage (e.g., above about 35 volts).

-   II. Housing

As indicated above, the capacitor element is hermetically sealed withina housing. Hermetic sealing typically occurs in the presence of agaseous atmosphere that contains at least one inert gas so as to inhibitoxidation of the solid electrolyte during use. The inert gas mayinclude, for instance, nitrogen, helium, argon, xenon, neon, krypton,radon, and so forth, as well as mixtures thereof. Typically, inert gasesconstitute the majority of the atmosphere within the housing, such asfrom about 50 wt. % to 100 wt. %, in some embodiments from about 75 wt.% to 100 wt. %, and in some embodiments, from about 90 wt. % to about 99wt. % of the atmosphere. If desired, a relatively small amount ofnon-inert gases may also be employed, such as carbon dioxide, oxygen,water vapor, etc. In such cases, however, the non-inert gases typicallyconstitute 15 wt. % or less, in some embodiments 10 wt. % or less, insome embodiments about 5 wt. % or less, in some embodiments about 1 wt.% or less, and in some embodiments, from about 0.01 wt. % to about 1 wt.% of the atmosphere within the housing. For example, the moisturecontent (expressed in terms of relatively humidity) may be about 10% orless, in some embodiments about 5% or less, in some embodiments about 1%or less, and in some embodiments, from about 0.01 to about 5%.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIG. 1, forexample, one embodiment of a capacitor assembly 100 is shown thatcontains a housing 122 and a capacitor element 120. In this particularembodiment, the housing 122 is generally rectangular. Typically, thehousing and the capacitor element have the same or similar shape so thatthe capacitor element can be readily accommodated within the interiorcavity. In the illustrated embodiment, for example, both the capacitorelement 120 and the housing 122 have a generally rectangular shape.

If desired, the capacitor assembly of the present invention may exhibita relatively high volumetric efficiency. To facilitate such highefficiency, the capacitor element typically occupies a substantialportion of the volume of an interior cavity of the housing. For example,the capacitor element may occupy about 30 vol. % or more, in someembodiments about 50 vol. % or more, in some embodiments about 60 vol. %or more, in some embodiments about 70 vol. % or more, in someembodiments from about 80 vol. % to about 98 vol. %, and in someembodiments, from about 85 vol. % to 97 vol. % of the interior cavity ofthe housing. To this end, the difference between the dimensions of thecapacitor element and those of the interior cavity defined by thehousing are typically relatively small,

Referring to FIG. 1, for example, the capacitor element 120 may have alength (excluding the length of the anode lead 6) that is relativelysimilar to the length of an interior cavity 126 defined by the housing122. For example, the ratio of the length of the anode to the length ofthe interior cavity ranges from about 0.40 to 1.00, in some embodimentsfrom about 0.50 to about 0.99, in some embodiments from about 0.60 toabout 0.99, and in some embodiments, from about 0.70 to about 0.98. Thecapacitor element 120 may have a length of from about 5 to about 10millimeters, and the interior cavity 126 may have a length of from about6 to about 15 millimeters. Similarly, the ratio of the height of thecapacitor element 120 (in the −z direction) to the height of theinterior cavity 126 may range from about 0.40 to 1.00, in someembodiments from about 0.50 to about 0.99, in some embodiments fromabout 0.60 to about 0.99, and in some embodiments, from about 0.70 toabout 0.98. The ratio of the width of the capacitor element 120 (in the−x direction) to the width of the interior cavity 126 may also rangefrom about 0.50 to 1.00, in some embodiments from about 0.60 to about0.99, in some embodiments from about 0.70 to about 0.99, in someembodiments from about 0.80 to about 0.98, and in some embodiments, fromabout 0.85 to about 0.95. For example, the width of the capacitorelement 120 may be from about 2 to about 7 millimeters and the width ofthe interior cavity 126 may be from about 3 to about 10 millimeters, andthe height of the capacitor element 120 may be from about 0.5 to about 2millimeters and the width of the interior cavity 126 may be from about0.7 to about 6 millimeters.

Although by no means required, the capacitor element may be attached tothe housing in such a manner that an anode termination and cathodetermination are formed external to the housing for subsequentintegration into a circuit. The particular configuration of theterminations may depend on the intended application. In one embodiment,for example, the capacitor assembly may be formed so that it is surfacemountable, and yet still mechanically robust. For example, the anodelead may be electrically connected to external, surface mountable anodeand cathode terminations (e.g., pads, sheets, plates, frames, etc.).Such terminations may extend through the housing to connect with thecapacitor. The thickness or height of the terminations is generallyselected to minimize the thickness of the capacitor assembly. Forinstance, the thickness of the terminations may range from about 0.05 toabout 1 millimeter, in some embodiments from about 0.05 to about 0.5millimeters, and from about 0.1 to about 0.2 millimeters. If desired,the surface of the terminations may be electroplated with nickel,silver, gold, tin, etc. as is known in the art to ensure that the finalpart is mountable to the circuit board. In one particular embodiment,the termination(s) are deposited with nickel and silver flashes,respectively, and the mounting surface is also plated with a tin solderlayer. In another embodiment, the termination(s) are deposited with thinouter metal layers (e.g., gold) onto a base metal layer (e.g., copperalloy) to further increase conductivity.

In certain embodiments, connective members may be employed within theinterior cavity of the housing to facilitate connection to theterminations in a mechanically stable manner. For example, referringagain to FIG. 1, the capacitor assembly 100 may include a connectionmember 162 that is formed from a first portion 167 and a second portion165. The connection member 162 may be formed from conductive materialssimilar to the external terminations. The first portion 167 and secondportion 165 may be integral or separate pieces that are connectedtogether, either directly or via an additional conductive element (e.g.,metal). In the illustrated embodiment, the second portion 165 isprovided in a plane that is generally parallel to a lateral direction inwhich the lead 6 extends (e.g., −y direction). The first portion 167 is“upstanding” in the sense that it is provided in a plane that isgenerally perpendicular the lateral direction in which the lead 6extends. In this manner, the first portion 167 can limit movement of thelead 6 in the horizontal direction to enhance surface contact andmechanical stability during use. If desired, an insulative material 7(e.g., Teflon™ washer) may be employed around the lead 6.

The first portion 167 may possess a mounting region (not shown) that isconnected to the anode lead 6. The region may have a “U-shape” forfurther enhancing surface contact and mechanical stability of the lead6. Connection of the region to the lead 6 may be accomplished using anyof a variety of known techniques, such as welding, laser welding,conductive adhesives, etc. In one particular embodiment, for example,the region is laser welded to the anode lead 6. Regardless of thetechnique chosen, however, the first portion 167 can hold the anode lead6 in substantial horizontal alignment to further enhance the dimensionalstability of the capacitor assembly 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the connective member 162 and capacitor element 120 areconnected to the housing 122 through anode and cathode terminations 127and 129, respectively. More specifically, the housing 122 of thisembodiment includes an outer wall 123 and two opposing sidewalls 124between which a cavity 126 is formed that includes the capacitor element120. The outer wall 123 and sidewalls 124 may be formed from one or morelayers of a metal, plastic, or ceramic material such as described above.In this particular embodiment, the anode termination 127 contains afirst region 127 a that is positioned within the housing 122 andelectrically connected to the connection member 162 and a second region127 b that is positioned external to the housing 122 and provides amounting surface 201. Likewise, the cathode termination 129 contains afirst region 129 a that is positioned within the housing 122 andelectrically connected to the solid electrolyte of the capacitor element120 and a second region 129 b that is positioned external to the housing122 and provides a mounting surface 203. It should be understood thatthe entire portion of such regions need not be positioned within orexternal to the housing.

In the illustrated embodiment, a conductive trace 127 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. Similarly, a conductive trace 129 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. The conductive traces and/or regions of theterminations may be separate or integral. In addition to extendingthrough the outer wall of the housing, the traces may also be positionedat other locations, such as external to the outer wall. Of course, thepresent invention is by no means limited to the use of conductive tracesfor forming the desired terminations.

Regardless of the particular configuration employed, connection of theterminations 127 and 129 to the capacitor element 120 may be made usingany known technique, such as welding, laser welding, conductiveadhesives, etc. In one particular embodiment, for example, a conductiveadhesive 131 is used to connect the second portion 165 of the connectionmember 162 to the anode termination 127. Likewise, a conductive adhesive133 is used to connect the cathode of the capacitor element 120 to thecathode termination 129. The conductive adhesives may be formed fromconductive metal particles contained with a resin composition. The metalparticles may be silver, copper, gold, platinum, nickel, zinc, bismuth,etc. The resin composition may include a thermoset resin (e.g., epoxyresin), curing agent (e.g., acid anhydride), and coupling agent (e.g.,silane coupling agents). Suitable conductive adhesives are described inU.S. Patent Application Publication No. 2006/0038304 to Osako, et al.,which is incorporated herein in its entirety by reference thereto forall purposes.

Optionally, a polymeric restraint may also be disposed in contact withone or more surfaces of the capacitor element, such as the rear surface,front surface, upper surface, lower surface, side surface(s), or anycombination thereof. The polymeric restraint can reduce the likelihoodof delamination by the capacitor element from the housing. In thisregard, the polymeric restraint may possesses a certain degree ofstrength that allows it to retain the capacitor element in a relativelyfixed positioned even when it is subjected to vibrational forces, yet isnot so strong that it cracks. For example, the restraint may possess atensile strength of from about 1 to about 150 Megapascals (“MPa”), insome embodiments from about 2 to about 100 MPa, in some embodiments fromabout 10 to about 80 MPa, and in some embodiments, from about 20 toabout 70 MPa, measured at a temperature of about 25° C. It is normallydesired that the restraint is not electrically conductive.

Although any of a variety of materials may be employed that have thedesired strength properties noted above, curable thermosetting resinshave been found to be particularly suitable for use in the presentinvention. Examples of such resins include, for instance, epoxy resins,polyimides, melamine resins, urea-formaldehyde resins, polyurethanes,silicone polymers, phenolic resins, etc. In certain embodiments, forexample, the restraint may employ one or more polyorganosiloxanes.Silicon-bonded organic groups used in these polymers may containmonovalent hydrocarbon and/or monovalent halogenated hydrocarbon groups.Such monovalent groups typically have from 1 to about 20 carbon atoms,preferably from 1 to 10 carbon atoms, and are exemplified by, but notlimited to, alkyl (e.g., methyl, ethyl, propyl, pentyl, octyl, undecyl,and octadecyl); cycloalkyl (e.g., cyclohexyl); alkenyl (e.g., vinyl,allyl, butenyl, and hexenyl); aryl (e.g., phenyl, tolyl, xylyl, benzyl,and 2-phenylethyl); and halogenated hydrocarbon groups (e.g.,3,3,3-trifluoropropyl, 3-chloropropyl, and dichlorophenyl). Typically,at least 50%, and more preferably at least 80%, of the organic groupsare methyl. Examples of such methylpolysiloxanes may include, forinstance, polydimethylsiloxane (“PDMS”), polymethylhydrogensiloxane,etc. Still other suitable methyl polysiloxanes may includedimethyidiphenylpolysiloxane, dimethyl/methylphenylpolysiloxane,polymethylphenylsiloxane, methylphenyl/dimethylsiloxane, vinyldimethylterminated polydimethylsiloxane, vinylmethyl/dimethylpolysiloxane,vinyldimethyl terminated vinylmethyl/dimethylpolysiloxane, divinylmethylterminated polydimethylsiloxane, vinylphenylmethyl terminatedpolydimethylsiloxane, dimethylhydro terminated polydimethylsiloxane,methylhydro/dimethylpolysiloxane, methylhydro terminatedmethyloctylpolysiloxane, methylhydro/phenylmethyl polysiloxane, etc.

The organopolysiloxane may also contain one more pendant and/or terminalpolar functional groups, such as hydroxyl, epoxy, carboxyl, amino,alkoxy, methacrylic, or mercapto groups, which impart some degree ofhydrophilicity to the polymer. For example, the organopolysiloxane maycontain at least one hydroxy group, and optionally an average of atleast two silicon-bonded hydroxy groups (silanol groups) per molecule.Examples of such organopolysiloxanes include, for instance,dihydroxypolydimethylsiloxane,hydroxy-trimethylsiloxypolydimethylsiloxane, etc. Other examples ofhydroxyl-modified organopolysiloxanes are described in U.S. PatentApplication Publication No. 2003/0105207 to Kleyer, et al., which isincorporated herein in its entirety by reference thereto for allpurposes. Alkoxy-modified organopolysiloxanes may also be employed, suchas dimethoxypolydimethylsiloxane,methoxy-trimethylsiloxypolydimethylsiloxane,diethoxypolydimethylsiloxane,ethoxy-trimethylsiloxy-polydimethylsiloxane, etc. Still other suitableorganopolysiloxanes are those modified with at least one aminofunctional group. Examples of such amino-functional polysiloxanesinclude, for instance, diamino-functional polydimethylsiloxanes. Variousother suitable polar functional groups for organopolysiloxanes are alsodescribed in U.S. Patent Application Publication No. 2010/00234517 toPlantenberg, et al., which is incorporated herein in its entirety byreference thereto for all purposes.

Epoxy resins are also particularly suitable for use as the polymericrestraint. Examples of suitable epoxy resins include, for instance,glycidyl ether type epoxy resins, such as bisphenol A type epoxy resins,bisphenol F type epoxy resins, phenol novolac type epoxy resins,orthocresol novolac type epoxy resins, brominated epoxy resins andbiphenyl type epoxy resins, cyclic aliphatic epoxy resins, glycidylester type epoxy resins, glycidylamine type epoxy resins, cresol novolactype epoxy resins, naphthalene type epoxy resins, phenol aralkyl typeepoxy resins, cyclopentadiene type epoxy resins, heterocyclic epoxyresins, etc. Still other suitable conductive adhesive resins may also bedescribed in U.S. Patent Application Publication No. 2006/0038304 toOsako, et al, and U.S. Pat. No. 7,554,793 to Chacko, which areincorporated herein in their entirety by reference thereto for allpurposes.

If desired, curing agents may also be employed in the polymericrestraint to help promote curing. The curing agents typically constitutefrom about 0.1 to about 20 wt. % of the restraint. Exemplary curingagents include, for instance, amines, peroxides, anhydrides, phenolcompounds, silanes, acid anhydride compounds and combinations thereof.Specific examples of suitable curing agents are dicyandiamide, 1-(2cyanoethyl) 2-ethyl-4-methylimidazole, 1-benzyl 2-methylimidazole, ethylcyano propyl imidazole, 2-methylimidazole, 2-phenylimidazole,2-ethyl-4-methylimidazole, 2-undecylimidazole,1-cyanoethyl-2-methylimidazole, 2,4-dicyano-6,2-methylimidazolyl-(1)-ethyl-s-triazine, and2,4-dicyano-6,2-undecylimidazolyl-(1)-ethyl-s-triazine, imidazoliumsalts (such as 1-cyanoethyl-2-undecylimidazolium trimellitate,2-methylimidazolium isocyanurate, 2-ethyl-4-methylimidazoliumtetraphenylborate, and 2-ethyl-1,4-dimethylimidazoliumtetraphenylborate, etc. Still other useful curing agents includephosphine compounds, such as tributylphosphine, triphenylphosphine,tris(dimethoxyphenyl)phosphine, tris(hydroxypropyl)phosphine, andtris(cyanoethyl)phsphine; phosphonium salts, such astetraphenylphosphonium-tetraphenylborate,methyltributylphosphonium-tetraphenylborate, andmethyltricyanoethylphosphonium tetraphenylborate); amines, such as2,4,6-tris(dimethylaminomethyl)phenol, benzylmethylamine,tetramethylbutylguanidine, N-methylpiperazine, and2-dimethylamino-1-pyrroline; ammonium salts, such as triethylammoniumtetraphenylborate; diazabicyclo compounds, such as1,5-diazabicyclo[5,4,0]-7-undecene, 1,5-diazabicyclo[4,3,0]-5-nonene,and 1,4-diazabicyclo[2,2,2]-octane; salts of diazabicyclo compounds suchas tetraphenylborate, phenol salt, phenolnovolac salt, and2-ethylhexanoic acid salt; and so forth.

Still other additives may also be employed, such as photoinitiators,viscosity modifiers, suspension aiding agents, pigments, stress reducingagents, coupling agents (e.g., silane coupling agents), nonconductivefillers (e.g., clay, silica, alumina, etc.), stabilizers, etc. Suitablephotoinitiators may include, for instance, benzoin, benzoin methylether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isobutylether, 2,2 dihydroxy-2-phenylacetophenone,2,2-dimethoxy-2-phenylacetophenone 2,2-diethoxy-2-phenylacetophenone,2,2-diethoxyacetophenone, benzophenone, 4,4-bisdialylaminobenzophenone,4-dimethylaminobenzoic acid, alkyl 4-dimethylaminobenzoate,2-ethylanthraquinone, xanthone, thioxanthone, 2-cholorothioxanthone,etc. When employed, such additives typically constitute from about 0.1to about 20 wt. % of the total composition.

Referring again to FIG. 1, for instance, one embodiment is shown inwhich a single polymeric restraint 197 is disposed in contact with anupper surface 181 and rear surface 177 of the capacitor element 120.While a single restraint is shown in FIG. 1, it should be understoodthat separate restraints may be employed to accomplish the samefunction. In fact, more generally, any number of polymeric restraintsmay be employed to contact any desired surface of the capacitor element.When multiple restraints are employed, they may be in contact with eachother or remain physically separated. For example, in one embodiment, asecond polymeric restraint (not shown) may be employed that contacts theupper surface 181 and front surface 179 of the capacitor element 120.The first polymeric restraint 197 and the second polymeric restraint(not shown) may or may not be in contact with each other. In yet anotherembodiment, a polymeric restraint may also contact a lower surface 183and/or side surface(s) of the capacitor element 120, either inconjunction with or in lieu of other surfaces.

Regardless of how it is applied, it is typically desired that thepolymeric restraint is also in contact with at least one surface of thehousing to help further mechanically stabilize the capacitor elementagainst possible delamination. For example, the restraint may be incontact with an interior surface of one or more sidewall(s), outer wall,lid, etc. In FIG. 1, for example, the polymeric restraint 197 is incontact with an interior surface 107 of sidewall 124 and an interiorsurface 109 of outer wall 123. While in contact with the housing, it isnevertheless desired that at least a portion of the cavity defined bythe housing remains unoccupied to allow for the inert gas to flowthrough the cavity and limit contact of the solid electrolyte withoxygen. For example, at least about 5% of the cavity volume typicallyremains unoccupied by the capacitor element and polymer restraint, andin some embodiments, from about 10% to about 50% of the cavity volume.

Once connected in the desired manner, the resulting package ishermetically sealed as described above. Referring again to FIG. 1, forinstance, the housing 122 may also include a lid 125 that is placed onan upper surface of side walls 124 after the capacitor element 120 andthe polymer restraint 197 are positioned within the housing 122. The lid125 may be formed from a ceramic, metal (e.g., iron, copper, nickel,cobalt, etc., as well as alloys thereof), plastic, and so forth. Ifdesired, a sealing member 187 may be disposed between the lid 125 andthe side walls 124 to help provide a good seal. In one embodiment, forexample, the sealing member may include a glass-to-metal seal, Kovar®ring (Goodfellow Camridge, Ltd.), etc. The height of the side walls 124is generally such that the lid 125 does not contact any surface of thecapacitor element 120 so that it is not contaminated. The polymericrestraint 197 may or may not contact the lid 125. When placed in thedesired position, the lid 125 is hermetically sealed to the sidewalls124 using known techniques, such as welding (e.g., resistance welding,laser welding, etc.), soldering, etc. Hermetic sealing generally occursin the presence of inert gases as described above so that the resultingassembly is substantially free of reactive gases, such as oxygen orwater vapor.

It should be understood that the embodiments described are onlyexemplary, and that various other configurations may be employed in thepresent invention for hermetically sealing a capacitor element within ahousing. Referring to FIG. 2, for instance, another embodiment of acapacitor assembly 200 is shown that employs a housing 222 that includesan outer wall 123 and a lid 225 between which a cavity 126 is formedthat includes the capacitor element 120 and polymeric restraint 197. Thelid 225 includes an outer wall 223 that is integral with at least onesidewall 224. In the illustrated embodiment, for example, two opposingsidewalls 224 are shown in cross-section. The outer walls 223 and 123both extend in a lateral direction (−y direction) and are generallyparallel with each other and to the lateral direction of the anode lead6. The sidewall 224 extends from the outer wall 223 in a longitudinaldirection that is generally perpendicular to the outer wall 123. Adistal end 500 of the lid 225 is defined by the outer wall 223 and aproximal end 501 is defined by a lip 253 of the sidewall 224.

The lip 253 extends from the sidewall 224 in the lateral direction,which may be generally parallel to the lateral direction of the outerwall 123. The angle between the sidewall 224 and the lip 253 may vary,but is typically from about 60° to about 120°, in some embodiments fromabout 70° to about 110°, and in some embodiments, from about 80° toabout 100° (e.g., about 90°). The lip 253 also defines a peripheral edge251, which may be generally perpendicular to the lateral direction inwhich the lip 253 and outer wall 123 extend. The peripheral edge 251 islocated beyond the outer periphery of the sidewall 224 and may begenerally coplanar with an edge 151 of the outer wall 123. The lip 253may be sealed to the outer wall 123 using any known technique, such aswelding (e.g., resistance or laser), soldering, glue, etc. For example,in the illustrated embodiment, a sealing member 287 is employed (e.g.,glass-to-metal seal, Kovar® ring, etc.) between the components tofacilitate their attachment. Regardless, the use of a lip describedabove can enable a more stable connection between the components andimprove the seal and mechanical stability of the capacitor assembly.

Still other possible housing configurations may be employed in thepresent invention. For example, FIG. 3 shows a capacitor assembly 300having a housing configuration similar to that of FIG. 2, except thatterminal pins 327 b and 329 b are employed as the external terminationsfor the anode and cathode, respectively. More particularly, the terminalpin 327 a extends through a trace 327 c formed in the outer wall 323 andis connected to the anode lead 6 using known techniques (e.g., welding).An additional section 327 a may be employed to secure the pin 327 b.Likewise, the terminal pin 329 b extends through a trace 329 c formed inthe outer wall 323 and is connected to the cathode via a conductiveadhesive 133 as described above.

The embodiments shown in FIGS. 1-3 are discussed herein in terms of onlya single capacitor element. It should also be understood, however, thatmultiple capacitor elements may also be hermetically sealed within ahousing. The multiple capacitor elements may be attached to the housingusing any of a variety of different techniques, Referring to FIG. 4, forexample one particular embodiment of a capacitor assembly 400 thatcontains two capacitor elements is shown and will now be described inmore detail, More particularly, the capacitor assembly 400 includes afirst capacitor element 420 a in electrical communication with a secondcapacitor element 420 b. In this embodiment, the capacitor elements arealigned so that their major surfaces are in a horizontal configuration.That is, a major surface of the capacitor element 420 a defined by itswidth (−x direction) and length (−y direction) is positioned adjacent toa corresponding major surface of the capacitor element 420 b. Thus, themajor surfaces are generally coplanar. Alternatively, the capacitorelements may be arranged so that their major surfaces are not coplanar,but perpendicular to each other in a certain direction, such as the −zdirection or the −x direction. Of course, the capacitor elements neednot extend in the same direction.

The capacitor elements 420 a and 420 b are positioned within a housing422 that contains an outer wall 423 and sidewalls 424 and 425 thattogether define a cavity 426. Although not shown, a lid may be employedthat covers the upper surfaces of the sidewalls 424 and 425 and sealsthe assembly 400 as described above. Optionally, a polymeric restraintmay also be employed to help limit the vibration of the capacitorelements. In FIG. 4, for example, separate polymer restraints 497 a and497 b are positioned adjacent to and in contact with the capacitorelements 420 a and 420 b, respectively. The polymer restraints 497 a and497 b may be positioned in a variety of different locations. Further,one of the restraints may be eliminated, or additional restraints may beemployed. In certain embodiments, for example, it may be desired toemploy a polymeric restraint between the capacitor elements to furtherimprove mechanical stability.

In addition to the capacitor elements, the capacitor assembly alsocontains an anode termination to which anode leads of respectivecapacitor elements are electrically connected and a cathode terminationto which the cathodes of respective capacitor elements are electricallyconnected. Referring again to FIG. 4, for example, the capacitorelements are shown connected in parallel to a common cathode termination429. In this particular embodiment, the cathode termination 429 isinitially provided in a plane that is generally parallel to the bottomsurface of the capacitor elements and may be in electrical contact withconductive traces (not shown). The capacitor assembly 400 also includesconnective members 427 and 527 that are connected to anode leads 407 aand 407 b, respectively, of the capacitor elements 420 a and 420 b. Moreparticularly, the connective member 427 contains an upstanding portion465 and a planar portion 463 that is in connection with an anodetermination (not shown). Likewise, the connective 527 contains anupstanding portion 565 and a planar portion 563 that is in connectionwith an anode termination (not shown). Of course, it should beunderstood that a wide variety of other types of connection mechanismsmay also be employed.

The present invention may be better understood by reference to thefollowing examples.

Test Procedures Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C.±2° C.

Capacitance and Dissipation Factor

The capacitance and dissipation factor may be measured using a Keithley3330 Precision LCZ meter with Kelvin Leads with 2.2 volt DC bias and a0.5 volt peak to peak sinusoidal signal. The operating frequency may be120 Hz and the temperature may be 23° C.±2° C.

Leakage Current:

Leakage current (“DCL”) may be measured using a leakage test set thatmeasures leakage current at a temperature of 23°±2° C., 85°±2° C. and125°±2° C. and at the rated voltage for 10, 20, 30, 40, 50, 60, and 300seconds.

EXAMPLE 1

34,000 μFV/g tantalum powder was used to form anode samples. Each anodesample was embedded with a tantalum wire, sintered at 1800° C., andpressed to a density of 5.6 g/cm³. The resulting pellets had a size of5.20×3.70×0.85 mm. The pellets were anodized to 70V in awater/phosphoric acid electrolyte (conductivity 8.6 mS) at a temperatureof 85° C. to form the dielectric layer. The pellets were anodized againto 160V in water/boric acid/disodium tetraborate (conductivity 2.0 mS)at a temperature of 30° C. for 30 seconds to form a thicker oxide layerbuilt up on the outside. A conductive polymer coating was then formed bydipping the anodes into a dispersed poly(3,4-ethylenedioxythiophene)having a solids content 1.1% and viscosity 20 mPa·s (Clevios™ K, H. C.Starck). Upon coating, the parts were dried at 125° C. for 20 minutes.This process was repeated 10 times. Thereafter, the parts were dippedinto a dispersed poly(3,4-ethylenedioxythiophene) having a solidscontent 2% and viscosity 20 mPa·s (Clevios™ K, H. C. Starck). Uponcoating, the parts were dried at 125° C. for 20 minutes. This processwas not repeated. Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 2% andviscosity 160 mPa·s (Clevios™ K, H. C. Starck). Upon coating, the partswere dried at 125° C. for 20 minutes. This process was repeated 8 times.The parts were then dipped into a graphite dispersion and dried.Finally, the parts were dipped into a silver dispersion and dried.

The tantalum wire of the capacitor element was then laser welded to ananode connective member, The anode and cathode connective members werethen glued to a gold cathode termination and welded to a gold anodetermination located inside a ceramic housing having a length of 11.00mm, a width of 6.00 mm, and a thickness of 2.20 mm. The housing had goldplated solder pads on the bottom inside part of ceramic housing. Theadhesive employed for the cathode connection was a silver paste (EPO-TekE3035) and the adhesive was applied only between the leadframe portionsand gold plated solder pad. The welding employed for the anodeconnection was a resistance welding and an energy of 190 W was appliedbetween the leadframe portions and ceramic housing gold plated solderpad during 90 ms. The assembly was then loaded in a convection oven tosolder the paste. After that, a Kovar® lid having a length of 9.95 mm, awidth of 4.95 mm, and a thickness of 0.10 mm was placed over the top ofthe container, closely on the seal ring of the ceramic housing (Kovar®ring having a thickness of 0.30 mm) so that there was no direct contactbetween the interior surface of the lid and the exterior surface of theattached capacitor. The resulting assembly was placed into a weldingchamber and purged with nitrogen gas for 120 minutes/150° C. before seamwelding between the seal ring and the lid was performed. No additionalburn-in or healing was performed after the seam welding. Multiple parts(25) of 33 μF/25V capacitors were made in this manner.

EXAMPLE 2

Capacitors were formed in the manner described in Example 1, except thata different conductive polymer coating was used. The conductive polymercoating was formed by dipping the anodes into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 1.1% andviscosity 20 mPa·s (Clevios™ K, H. C. Starck). Upon coating, the partswere dried at 125° C. for 20 minutes. This process was repeated 10times. Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 2% andviscosity 20 mPa·s (Clevios™ K, H. C. Starck) and additional 20% solidscontent of poly(ethylene glycol) with molecular weight 600 (SigmaAldrich®). Upon coating, the parts were dried at 125° C. for 20 minutes.This process was not repeated. Thereafter, the parts were dipped into adispersed poly(3,4-ethylenedioxythiophene) having a solids content 2%and viscosity 160 mPa·s (Clevios™ K, H. C. Starck). Upon coating, theparts were dried at 125° C. for 20 minutes. This process was repeated 8times. The parts were then dipped into a graphite dispersion and dried.The assembly process was the same as described in Example 1. Multipleparts (25) of 33 μF/25V capacitors were made in this manner.

The finished capacitors of Examples were then tested for electricalperformance. The median results of capacitance, Df and ESR and DCL areset forth below in Table 1-4. The wet capacitance was 38.0 μF.

TABLE 1 Electrical Properties Cap Dry/Wet Cap ESR [μF] [%] Df [mΩ]Example 1 30.14 79.3 0.11 90.70 Example 2 32.35 85.1 0.11 92.33

TABLE 2 Leakage Current [μA] @ 23 ± 2° C. 10 s 20 s 30 s 40 s 50 s 60 s300 s Exam- 1385.53 797.87 536.03 392.35 303.63 244.53 35.66 ple 1 Exam-11.47 4.71 2.74 1.85 1.37 1.07 0.15 ple 2

TABLE 3 Leakage Current [μA] @ 85 ± 2° C. 10 s 20 s 30 s 40 s 50 s 60 s300 s Exam- 29.59 15.79 10.68 7.57 5.81 4.66 1.61 ple 1 Exam- 1.61 0.960.72 0.57 0.50 0.44 0.18 ple 2

TABLE 4 Leakage Current [μA] @ 125 ± 2° C. 10 s 20 s 30 s 40 s 50 s 60 s300 s Exam- 10.51 5.95 4.49 3.81 3.40 3.11 2.14 ple 1 Exam- 3.21 1.991.50 1.22 1.04 0.91 0.33 ple 2

As indicated, the DCL characteristics are significantly lower whenpoly(ethylene glycol) is employed (Example 2).

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

1. A capacitor assembly comprising: a capacitor element comprising asintered porous anode body, a dielectric layer that overlies the anodebody, and a solid electrolyte overlying the dielectric layer; a housingthat defines an interior cavity within which the capacitor element ispositioned and hermetically sealed; an anode termination that is inelectrical connection with the anode body; and a cathode terminationthat is in electrical connection with the solid electrolyte; wherein thesolid electrolyte contains a first layer that overlies the dielectriclayer and a second layer that overlies the first layer, the first layercontaining a conductive polymer and the second layer containing ahydroxy-functional nonionic polymer and a conductive polymer.
 2. Thecapacitor assembly of claim 1, wherein the interior cavity has a gaseousatmosphere that contains an inert gas, and wherein inert gasesconstituted from about 50 wt. % to 100 wt. % of the gaseous atmosphere.3. The capacitor assembly of claim 1, further comprising a lead thatextends in a lateral direction from the porous anode body, wherein thelead is positioned within the interior cavity of the housing.
 4. Thecapacitor assembly of claim 3, further comprising a connective memberthat contains a first portion that is positioned generally perpendicularto the lateral direction of the anode lead and connected thereto.
 5. Thecapacitor assembly of claim 4, wherein the connective member furthercontains a second portion that is generally parallel to the lateraldirection in which the anode lead extends.
 6. The capacitor assembly ofclaim 5, wherein the second portion is positioned within the housing. 7.The capacitor assembly of claim 1, wherein the anode body is formed froma powder that contains tantalum, niobium, or an electrically conductiveoxide thereof.
 8. The capacitor assembly of claim 1, wherein theconductive polymer is poly(3,4-ethylenedioxythiophene).
 9. The capacitorassembly of claim 1, wherein the solid electrolyte comprises a pluralityof pre-polymerized conductive polymer particles.
 10. (canceled)
 11. Thecapacitor assembly of claim 1, wherein the conductive polymer containedin the second layer further comprises a plurality of pre-polymerizedconductive polymer particles.
 12. The capacitor assembly of claim 1,wherein the hydroxy-functional polymer is a polyalkylene ether.
 13. Thecapacitor assembly of claim 12, wherein the polyalkylene ether is apolyalkylene glycol.
 14. The capacitor assembly of claim 1, furthercomprising an external polymer coating that overlies the solidelectrolyte, wherein the external polymer coating contains a pluralityof pre-polymerized conductive polymer particles.
 15. The capacitorassembly of claim 14, wherein the external polymer coating contains afirst layer that overlies the solid electrolyte and a second layer thatoverlies the first layer, wherein the first layer contains acrosslinking agent and the second layer contains the pre-polymerizedconductive polymer particles.
 16. The capacitor assembly of claim 1,wherein the assembly exhibits a wet-to-dry capacitance of about 60% ormore.
 17. A method of forming a capacitor assembly that comprises acapacitor element comprising a sintered porous anode body, a dielectriclayer that overlies the anode body, and a solid electrolyte overlyingthe dielectric layer, the capacitor assembly further comprising ahousing that defines an interior cavity within which the capacitorelement is positioned and hermetically sealed, the method comprising:positioning the capacitor element within the interior cavity of thehousing; electrically connecting the anode body of the capacitor elementto an anode termination and the solid electrolyte of the capacitorelement to a cathode termination; and hermetically sealing the capacitorelement within the housing; wherein the solid electrolyte is formed by amethod that comprises forming a first layer that contains a conductivepolymer, and thereafter forming a second layer that overlies the firstlayer and contains a conductive polymer and a hydroxy-functionalnonionic polymer.
 18. (canceled)
 19. The method of claim 17, wherein thehydroxy-functional polymer is applied in the form of a dispersion thatcontains a plurality of pre-polymerized conductive polymer particles.20. The method of claim 17, wherein the hydroxy-functional nonionicpolymer is applied in the form of a solution.